The present invention relates to a method and apparatus for cold starting an internal combustion engine according.
Vehicles equipped with diesel or another lean burn engine offer the benefit of increased fuel economy, however, control of nitrogen oxide (NOx) emissions from such engines is needed due to the high content of oxygen in the exhaust gas. In this regard, Selective Catalytic
Reduction (SCR) catalysts, in which NOx is continuously removed through active injection of a reductant, such as urea, into the exhaust gas mixture entering the catalyst, are known to achieve high NOx conversion efficiency.
However, exhaust gas after treatment systems (EATS or EGAS) need to reach a specific operating temperature before they become active. Therefore, a considerable amount of the overall quantity of pollutants emitted to the atmosphere during a journey is discharged at a very limited period of time during cold start conditions.
To reduce the pollution during such cold start conditions it is desirable to minimize the time required for the exhaust gas after treatment system to reach its operating temperature. Conventionally, this is done by increasing the load on the engine during cold start conditions.
However, a higher load requires more fuel which may lead to increased production of pollution, which is contrary to the desired reduction in emissions.
It is desirable to provide a method for cold starting an internal combustion engine that reduces the fuel consumption and at the same time reduces the pollution.
According to a first aspect of the invention it is provided a method for achieving reduced emissions at cold start of an internal combustion engine having an exhaust gas after treatment system comprising at least one Diesel Oxygen Catalyst (DOC), at least one Diesel Particulate Filter (DPF) and a Selective Catalytic Reduction (SCR) unit. The method comprising the steps of: heating the DOC prior to cold starting said internal combustion engine, starting and controlling the internal combustion engine towards a predetermined limit value of NOx emission when said DOC has reached a predetermined DOC temperature, optimizing fuel consumption at a predetermined total emission level when said DPF and SCR have reached a predetermined temperature.
In another example embodiment of the present invention said heating of said DOC prior to starting said internal combustion engine is performed by cranking the internal combustion engine with an electric device with the fuel supply to said internal combustion engine shut off and with a setting chosen of the internal combustion engine so that air coming out from an outlet valve of a cylinder is higher in temperature than incoming air through an inlet valve of said cylinder.
The advantage with this embodiment is that the heating may be performed by built in devices only, for example in hybrid vehicles the means for cranking the engine may be the electric power source and the setting chosen for the internal combustion engine may be alteration of the closure and opening time of the exhaust valve.
In yet another example embodiment of the present invention said predetermined limit value of NOx emission is achieved by using HCCI combustion principle.
An advantage of this embodiment is that the engine may be run at relatively low temperatures of the EATS and nevertheless fulfill the prevailing pollution requirements.
In still another example embodiment of the present invention said predetermined limit value of NOx emission is achieved by using at least 50% EGR.
An advantage of this embodiment is that the EGR regulation may be used to control the NOx emission at the same time as it is used for decreasing the combustion temperature in HCCI mode or PHCCI mode.
In still another example embodiment of the present invention said heating of said DOC is performed while a vehicle, in which said internal combustion engine is provided, is moving.
An advantage with this embodiment is that the heating is not necessarily performed while the vehicle is standing still and may therefore save time for the driver.
Another advantage may be that the momentum of the vehicle may be used as another source of providing energy to the means for heating the DOC.
In still another example embodiment of the present invention said heating of said DOC is performed while a vehicle, in which said internal combustion engine is provided, is standing still.
An advantage of this embodiment is that the heating is not dependent on the driving condition of the vehicle.
In still another example embodiment of the present invention said setting is an adjustment of the exhaust valve to perform exhaust braking.
An advantage of this embodiment is that existing technology may be used for heating the EATS which is not dependent upon the driving condition for the vehicle.
In still another example embodiment the present invention further comprising the step of: providing a HC-trap, a NOx-trap and a bypass channel with a valve between said DOC and said DPF, closing said bypass valve until said DOC has reached said predetermined temperature, opening said bypass valve when said DOC is at and above said predetermined temperature, closing said bypass valve when an operator requires an engine with a NOx value above the predetermined value when said SCR is below a predetermined temperature.
An advantage of this embodiment is that the regulation of the exhaust gases, and thereby regulating its temperature, may be performed in the EATS by itself either in combination with another heating source or by itself.
In a second aspect of the present invention it is provided a device for achieving reduced emissions at cold start of an internal combustion engine having an exhaust gas after treatment system (EGAS) comprising at least one Diesel Oxygen Catalyst (DOC), at least one Diesel
Particulate Filter (DPF) and a Selective Catalytic Reduction (SCR) unit. Said device further comprising a HC trap, a NOx trap and a bypass channel with a valve provided between said DOC and said DPF.
An advantage of this embodiment is that temperature regulation for different units in the EGAS can be done in the unit itself.
In another example embodiment of the present invention said HC-trap and said NOx-trap is provided as separate units.
An advantage with this embodiment is that each trap may be optimized independently of the other trap.
In another example embodiment of the present invention said NOx-trap material is coated on said HC-trap material.
An advantage with this embodiment is that the traps may be compact and therefore requires small space which in turn may reduce the overall size of the EGAS.
In a third aspect of the present invention it is provided a device for achieving reduced emissions at cold start of an internal combustion engine having an exhaust gas after treatment system comprising at least one Diesel Oxygen Catalyst (DOC) at least one Diesel Particulate Filter (DPF) and a Selective Catalytic Reduction (SCR) unit, further comprising: means for beating the DOC prior to cold starting said internal combustion engine, means for starting and controlling the internal combustion engine towards a predetermined limit value of NOx emission when said DOC has reached a predetermined DOC temperature, means for optimizing fuel consumption at a predetermined total emission level when said DPF and SCR have reached a predetermined temperature.
In another example embodiment of the present invention said means for heating of said DOC prior to starting said internal combustion engine is an electric device for cranking the internal combustion engine with the fuel supply to said internal combustion engine shut off and with a setting chosen of the internal combustion engine so that air coming out from an outlet valve of a cylinder is higher in temperature than incoming air through an inlet valve of said cylinder.
The advantage with this embodiment is that the heating may be performed by built in devices only, for example in hybrid vehicles the means for cranking the engine may be the electric power source and the setting chosen for the internal combustion engine may be alteration of the closure and opening time of the exhaust valve.
In another example embodiment of the present invention said device further comprising between said DOC and said DPF a HC-trap, a NOx-trap and a bypass channel with a valve, means for closing said bypass valve until said DOC has reached said predetermined temperature, means for opening said bypass valve when said DOC is at and above said predetermined temperature, means for closing said bypass valve when an operator requires an engine with a NOx value above the predetermined value when said SCR is below a predetermined temperature.
An advantage of this embodiment is that temperature of the EGAS can be controlled by valves in the EGAS and adjustment of the exhaust valve independently of each other for achieving the desired temperature in a most efficient way.
In the drawings, equal or similar elements are referred to by equal reference numerals. The drawings are merely schematic representations, not intended to portray specific parameters of the invention.